there could be trouble with the severum and silver dollars. I tried that combo once and the SDs had to go to my dad's tank because the severum wouldn't stop beating the crap out of them.
severums and oscars are both S.american fish, sometimes that means they'll work, sometime that means problems. I'd do some searches with oscar and severum as the subject, maybe add in tankmates too. both here and google.
leporinus are supposed to be nippy fish and may not work with the oscar. I've had two, and neither were nippy, but that's the reputation they have at my local shops. I was there when someone tried trading one in for that reason, and that's why they wouldn't take him. beautiful fish though.